Why does oil burn when put into a hot pan?

Question

I was trying to make the scrambled eggs based on the answer found here. I set my stainless-steel pan on the burner and set the burner about halfway between medium and high. After the panned warmed on quite a bit (probably all the way), I put some ghee in the pan. It immediately burned and smoked up my home.

Why does ghee (and probably also other oils) burn when put into a hot pan? What is the remedy for this? According to some of the answers to this question, I should either be putting in the ghee (or oil) into a cold pan or warming it or putting it into the pan once it's slightly warm, but not hot.

I found the "Do you heat the pan first?" question somewhat helpful, but the answers don't really give scientific reasons for their responses. If ghee has a smoke point of 485 F, why would it burn just because it heats up rapidly?

Update: As noted in Cindy's answer, I didn't follow the instructions in the referenced question because I didn't put the ghee/oil in the pan before the pan got hot.

I'm still curious as to whether the ghee burned because the pan temperature was over the ghee's smoke point or because the ghee was heated too quickly by being put into a hot pan.

Answer 1

Yes, your pan was too hot.

Because your pan was empty when you heated it, it had minimal heat capacity, and could only lose heat by convection and radiation. Thus, it heated up quickly, and likely reached a much higher temperature than it normally could with food in it.

When you heat a pan with food in it, some of the heat is transferred to the food, and much of that heat is, in turn, lost when water in the food evaporates. This slows down the heating rate, and significantly reduces the peak temperature reached.

(Evaporating water is an extremely efficient method of heat transfer, especially at high temperatures, and even solid foods like meat and vegetables still contain quite a bit of water. Any time you put something on a hot pan and it steams or sizzles, that's the sign of water evaporating.)

Also, because you didn't have any oil or water or food on the pan, you had no easy way to gauge its temperature by eye. Normally, if you heat a pan with oil already in it, you can tell when it's hot enough just by looking at how the oil behaves. If you miss all the subtler signs, like the oil turning more runny and starting to form convection patterns, the point where it starts to change color and smoke is an unmistakable sign that you've definitely heated it too far.

With a dry pan, it's quite hard to tell just how hot it is. One trick I sometimes use is to sprinkle a few drops of water onto the pan and seeing how quickly it evaporates. (Don't do this if the pan already has oil in it!) When the drops evaporate all but instantly (but still briefly wet the surface, rather than exploding on contact or hovering over it), it's time to add the oil / butter.

Of course, the modern high-tech alternative would be to get an IR thermometer. I actually do have one, but I rarely use it — it's just quicker and easier to dip my fingers in some water and sprinkle it on the pan than to get the thermometer out of the cupboard.

Answer 2

You must have had your pan screaming hot in order for ghee to immediately burn. As you note, ghee has a pretty high smoke point (as do other clarified butters).

Additionally it would appear that you didn't follow the instructions in the link you referenced. It was not indicated to preheat the pan before adding oil, but to add the oil when the pan was placed on the burner and when it began to sizzle to add the eggs.

Regarding smoke point, the easy answer is that it is the temperature where oils and fats will start to break down and burn. There are a lot of things occurring when this happens but I won't even attempt to go into that as I'm not as science oriented as many others on the site. Smoke points vary greatly depending on the type of oil, thus the reason that some oils are better suited to certain applications.

Answer 3

Why does ghee (and probably also other oils) burn when put into a hot pan? What is the remedy for this?

As other people have pointed out, the issue here is the empty pan. To explain further:

I set my stainless-steel pan on the burner and set the burner about halfway between medium and high.

You did not say whether this is gas or electric. If it is gas, regardless of how high or low the flame is, the flame is the same temperature -- for natural gas this is close to 2000°C. It's unlikely you could actually get the pan that hot, of course, but the point is, the longer you leave it over the flame without anything beyond the pan to absorb it, the hotter the pan will get.

If the stove top is electric, a similar principle still applies. Although the elements are switched on and off in relation to the temperature of the element, it is easy to observe that even on low, the surface of contact clearly exceeds the smoke point of any oil, which is why grease that hits the element incinerates almost instantly. If you've ever left a clean, empty pan (e.g, one where water has boiled off...) on an electric stove (even on low) long enough, you'll be familiar with the scorched inner surface which can result. If you poured a small amount of oil into such a pan without letting it cool, I promise you will see a lot of smoke!

In short, although some stove top controls do have temperatures on them as rough guides, unlike an oven those do not indicate the maximum temperature of the cooking volume. Since heat conducts and rises, that's an impossible thing to regulate from the stove surface.

Answer 4

Almost any cooking ingredient* is organic material, which means that it contains carbon. Any such substance will burn if you make it hot enough and there's oxygen available, which there always is when there's a human cooking in the room. How hot is "hot enough" depends on the particular substance.

So, yes, your ghee burnt because it got too hot. And it's just the temperature that matters, not how quickly it was heated to that temperature.

 * The exceptions that come to mind are water, salt and baking soda.